The use of headphones by individuals for the purpose of listening to audio programs including music or for simply filtering the ambient noise in our environment has become ubiquitous. This is true to the development of the MP3 player as well as the utilization of such services as ITunes to download music. Individual's are traversing the streets with their headphones in place as well as using them while they are utilizing public transportation such as airplanes, commuter and long distance railroads, as well as buses. While the use of these headphones does give the individual enjoyment, there are problems involved with the utilization of these devices. For example, ambient noise such as is produced by other passengers using the various modes of public transportation while talking on cell phones or with other passengers, would make the use of these devices less enjoyable. This is due to the fact that the individual would hear a constant verbal barrage generated by these other passengers or the sounds of the various conveyances themselves, such as the humming of airplane or bus engines.
These problems have been alleviated somewhat through the utilization of an active noise reduction (ANR) system used in conjunction with the headphones. These headphones are not only provided with a loudspeaker for producing music or any other audio output, they are also provided with a microphone for sensing the ambient noise in the environment. The ANR includes circuitry for sensing this ambient noise through the microphone and producing a signal which has the same amplitude as the ambient noise but is 180° out of phase of that signal. A negative feedback loop is provided introducing both the ambient noise to the loop, as well as the sound wave produced by the ANR which is 180° out of phase with the ambient noise, thereby cancelling and eliminating the ambient noise, and consequently allowing an individual to enjoy only the audio output produced by the loudspeaker.
However, due to the very limited space in which both the microphone as well as the loudspeaker are housed, a problem relating to audio feedback has occurred. Audio feedback is produced when the sound from the loudspeaker is fed into the microphone, creating a high pitched electronic squeal which typically rises in volume until various adjustments are made. When the audio feedback is created with both the loudspeaker and the microphone situated in a relatively large enclosure, such as an auditorium, corrective action such as turning down the volume of the loudspeaker or the microphone would alleviate the problem. However, when the enclosed space in which the loudspeaker and the microphone are included, such as is provided in a standard headphone is very limited in size, it is more difficult to correct this problem. Due to this relatively small enclosure, the operating parameters of both the loudspeaker and the microphone are tuned to a very low tolerance of error. Consequently, if the enclosed space in which both the loudspeaker and the microphone are housed is reduced even slightly due to even inadvertent pressure applied to the ear muff of the headphone, the annoying high pitch squeal due to the audio feedback would be produced.